Web handling is an important issue in installations for processing continuous web. Therein, many coils handling hundreds of meters or even kilometers of web have to be arranged and operated in such a way that no damage, in particular unilateral thermal damages such as crinkles, trumlines, tear-offs, or the like occur in the web. However, the web thickness of, for instance, plastic or metal foils varies over the substrate width. Also, sometimes the web is wound up on the storage spool coil (also called “storage spool” herein) with a different inner tension over the web's width.
It is undesirable that failures occur during the web processing such as the web coating. These failures may lead to the total stop of production and/or to the rejection of parts or the entire web treated. In other words, a web guiding malfunction can be very expensive and time consuming.
In order to avoid malfunctions of a web processing apparatus it is known in the art to provide each guide roll of the web guiding apparatus with a specific tolerance. This way a difference up to, e.g. 0.02 mm in the web's thickness along the width of the web can be handled. However, in installations with long coiling length the addition of the guide roller bearing tolerances can cause a tilted feeding in the installation and may lead to a diagonal pull in the winding system. Further, in vacuum applications very small deviations in thickness can cause complications or failure which would not occur at ambient pressure.
Furthermore, there are considerable space constraints in today's web processing apparatuses, such as a coating apparatus. In addition, in many applications the web must not be touched or guided on one side of the web at all, namely, the coated side of the web or foil. Consequently, the design of the web's route through a web processing apparatus, such as a coating apparatus, is essentially limited. This is particularly true if, for instance, the coating step is performed by a coating drum resulting already in a 150° up to 180° consumption of the maximally 360° overall turnings that are available for the web's route.